Segmented superabrasive grinding device

ABSTRACT

The present invention is for a grinding device, such as a surface grinding disc or an annular grinding wheel, constructed from a plurality of abrasive segments arranged in an array thereon, wherein the plurality of abrasive segments are embedded in a matrix composition, and wherein the device is abapted to perform a “dry machining” operation. The abrasive segments may be resin bonded or vitrified and may include diamond or other superhard or superabrasive particles, such as, for example, cubic boron nitride (“cBN”), dispersed therein. Both the abrasive segments and the matrix composition include a dry lubricant, such as hexagonal boron nitride, molybdenum disulfide or graphite, dispersed therein. The abrasive segments further include a melt phase metal composition, such as bronze or other copper alloys, to aid in heat dissipation.

BACKGROUND OF THE INVENTION

The present invention relates to grinding devices, such as grindingdiscs and wheels. More particularly, the present invention relates togrinding devices, such as grinding discs and wheels, wherein thegrinding device is adapted to perform “dry machining” operations.

In the machining of substantially planar workpieces, such as brakerotors, power steering pump rings and rotors, valve plates, coil springends, and the like, it is known to pass the workpiece along the radial“face” surface of a surface grinding disc. For example, U.S. Pat. No.6,419,564 to Herrman, et al., teaches a surface grinding machine and asurface grinding disc used therewith to machine substantially flatworkpieces. In particular, Herrman '564 teaches a segmented grindingdisc constructed from a circular base to which a plurality of abrasivepieces are secured in a predefined array. The abrasive pieces arearranged so as to define spaces therebetween for the purpose of allowingcooling fluids to flow over, around, in between and away from theabrasive pieces, thereby flushing swarf from the abrasive pieces andfacilitating heat dissipation. According to one aspect of the presentinvention, it is desirable to provide a grinding device, such as, forexample, a surface grinding disc or an annular grinding wheel, whereinthe device includes a plurality of abrasive segments arranged in anarray thereon (or therearound, as the case may be).

Herrman '562 also teaches that the abrasive pieces may include diamondor superabrasive particles, such as cubic boron nitride (“cBN”)dispersed therein for reasons which are obvious to those of ordinaryskill in the art However, it is customary for machining operations beingperformed with such a superabrasive grinding device to require a flow ofcoolant to be directed thereover, as described in Herrman '564, for thepurposes discussed therein. For reasons that will be obvious to one ofordinary skill in the art, such “wet machining” operations areundesirable. It is desirable, therefore, to provide a grinding device,such as, for example, a surface grinding disc or an annular grindingwheel, constructed from a plurality of abrasive segments arranged in anarray thereon, wherein the abrasive segments include superabrasiveparticles dispersed therein, and wherein the device is adapted tooperate in a “dry machining” environment, that is, for example, withoutthe use of more than a nominal quantity of coolant or other lubricant.

The efficiency of conventional dry machining operations is limited bythe rate at which workpiece material may be removed therefrom withoutimparting workpiece failure or damage, such as, for example, burning.This is because coolants serve an important function of dissipating heatand dry machining is—by definition—machining in a dry or near-dryenvironment (i.e., without the use of coolants). It is desirabletherefore to provide a grinding device, such as, for example, a surfacegrinding disc or an annular grinding wheel, constructed from a pluralityof abrasive segments arranged in an array thereon, wherein the pluralityof abrasive segments are embedded in a matrix composition adapted toenhance heat dissipation.

It is desirable furthermore to provide a method of dry machiningworkpieces wherein the method provides a grinding device, such as, forexample, a surface grinding disc or an annular grinding wheel,constructed from a plurality of abrasive segments arranged in an arraythereon, wherein the plurality of abrasive segments are embedded in amatrix composition adapted to enhance heat dissipation.

It is also desirable to provide a method of dry machining workpieceswith increased machining efficiency, that is, for example, by increasingworkpiece material removal rates.

It is even furthermore desirable to provide a method of dry machiningworkpieces constructed from hard materials, which typically aredifficult to dry machine using known dry machining methods and devices.

SUMMARY OF THE INVENTION

The present invention is for a grinding device, such as a surfacegrinding disc or an annular grinding wheel, constructed from a pluralityof abrasive segments arranged in an array thereon, wherein the pluralityof abrasive segments are embedded in a matrix composition, and whereinthe device is adapted to perform a “dry machining” operation. Theabrasive segments may be resin bonded or vitrified and may includediamond or other superhard or superabrasive particles, such as, forexample, cubic boron nitride (“cBN”), dispersed therein. Both theabrasive segments and the matrix composition include a dry lubricant,such as hexagonal boron nitride, molybdenum disulphide or graphite,dispersed therein. The abrasive segments further include a melt phasemetal composition, such as bronze or other copper alloys, to aid in heatdissipation.

It is an object of the present invention to provide a grinding device,such as, for example, a surface grinding disc or an annular grindingwheel, wherein the device includes a plurality of abrasive segmentsarranged in an array thereon (or therearound, as the case may be).

It is another object of the present invention to provide a grindingdevice, such as, for example, a surface grinding disc or an annulargrinding wheel, constructed from a plurality of abrasive segmentsarranged in an array thereon, wherein the abrasive segments includesuperabrasive particles dispersed therein, and wherein the device isadapted to perform “dry machining” operations, that is, machiningoperations without the use of more than a nominal quantity of coolant orother lubricant.

It is still another object of the present invention to provide agrinding device, such as, for example, a surface grinding disc or anannular grinding wheel, constructed from a plurality of abrasivesegments arranged in an array thereon, wherein the plurality of abrasivesegments are embedded in a matrix composition adapted to enhance heatdissipation.

It is yet another object of the present invention to provide a method ofdry machining workpieces wherein the method provides a grinding device,such as, for example, a surface grinding disc or an annular grindingwheel, constructed from a plurality of abrasive segments arranged in anarray thereon, wherein the plurality of abrasive segments are embeddedin a matrix composition adapted to enhance heat dissipation.

It is also an object of the present invention to provide a method of drymachining workpieces with increased machining efficiency, that is, forexample, by increasing workpiece material removal rates.

It is still another object of the present invention to provide a methodof dry machining workpieces constructed from hard materials, whichtypically are difficult to dry machine using known dry machining methodsand devices.

These and other objects, features and advantages of the presentinvention become apparent to those of ordinary skill in the art from thedescription which follows, and may be realized by means of theinstrumentalities and combinations particularly pointed out therein, aswell as by those instrumentalities, combinations and improvementsthereof which are not described expressly therein, but which would beobvious to those of ordinary and reasonable skill in the art.

BRIEF DESCRIPTION OF THE DRAWINGS

A better understanding of the invention will be had upon reference tothe following description in conjunction with the accompanying drawingsin which like reference numerals represent like parts, and wherein:

FIG. 1 is a face view of a grinding device according to a preferredembodiment of the present invention;

FIG. 2 is an edge section view of the grinding device of FIG. 1, shownalong section line 2-2 of FIG. 1;

FIG. 3 is a partial section view of the grinding device of FIG. 1, shownalong section line 3-3 of FIG. 1;

FIG. 4 is a partial face view of a grinding device according to analternative embodiment of the present invention showing an alternativearrangement of abrasive segments on the device;

FIG. 5 is a face view of a grinding device according to an alternativeembodiment of the present invention; and,

FIG. 6 is a section view of the grinding device of FIG. 5, shown alongsection line 6-6 of FIG. 5.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention is for a grinding device, such as a surfacegrinding disc or an annular grinding wheel, constructed from a pluralityof abrasive segments arranged in an array thereon, wherein the pluralityof abrasive segments are embedded in a matrix composition, and whereinthe device is adapted to operate in a “dry machining” or “near-drymachining” environment.

With reference to FIGS. 1-3, a grinding device 10 according to apreferred embodiment of the present invention takes the form of asurface grinding disc suitable for machining substantially flatworkpieces, such as, for example, brake rotors, power steering pumprings and rotors, valve plates, coil spring ends, and the like. Thedevice 10 includes a circular rigid base 20, constructed from, forexample, aluminum or steel, one or more abrasive segments 30 (sometimesreferred to as “buttons”) secured within a matrix composition 40 whichis generally circular in shape and conterminous with the base 20.Segments 30 can be viewed as being “embedded” in the matrix composition40 and may be integrally formed therein or may be inserted into pockets(not shown) formed into the matrix 40 after the matrix has been securedto the base 20. Segments 30 are shown to have a thickness, which is forthe purpose of illustration only. Matrix 40 preferably extends to theperiphery 24 of the base 20, although it may extend only a portion overthe base 20 towards the periphery 24 thereof. In either case, matrix 40covers enough of the base 20 and surrounds each of the segments 30sufficiently to retain segments 30 thereby. Although segments 30 areshown in FIG. 1 arranged in a circular array forming an array path 26concentric with the device 10, segments 30 may, alternatively, bearranged in some other array.

For example, referring to FIG. 4, a portion of the device is shownwherein segments 30 are depicted to be arranged along two concentricpaths 26, 26′ in abutting relation to one another. Any number of paths,concentric or non-concentric, may be provided without departing fromeither the spirit or the scope of the present invention. Moreover,segments 30 may be spaced from one another, thereby providing additionalmatrix composition 40 therebetween It should be pointed out that thepresent invention is not limited to any particular size, shape orarrangement of segments 30. Thus, non-circular segments, for example,may be used according to the present invention and not depart fromeither the spirit or the scope thereof. Similarly, not all segments 30provided on a grinding device 10 need to possess the same size, shape orarrangement as any other segment 30 provided on that device 10. Forexample, a device 10 may include circular segments 30 in one regionthereof and triangular, rectangular, hexagonal or arcuate segments inanother region thereof.

Even further, segments 30 need not be provided near the periphery 24 ofthe device 10, as shown and depicted in the Figures. For the purpose ofillustration, however, segments 30 are circular in shape and have adiameter between ¼ in. and 1½ in. Each segment 30 is spaced fromadjacent segments 30 by a distance no greater than ½ of the shortestdimension of the workpiece to be machined thereby.

Referring back to FIG. 3, the matrix 40 is formed so that an exposedsurface 42 thereof is substantially coplanar with an abrasive face 32 ofthe segments 30, thereby defining a substantially continuous planar faceof the device 10. Using conventional means, workpieces (not shown) arebrought into contact with the face of the device and advanced therealongto machine a substantially flat surface of or into the workpiece.

Turning now to the composition of the segments 30, the followingcompositions and ranges thereof are provided for the purpose ofillustration only. Generally stated, according to one aspect of thepresent invention, a grinding device is provided having abrasivesegments comprising: 1) a superabrasive material, such as cBN; 2) aresin bond, such as a polyimide resin; 3) a refractory, non-grindingabrasive grain, such as boron carbide (“BC”); 4) a heat-dissipativemelt-phase metal, such as a copper-tin (i.e., bronze) alloy; and, 5) adry lubricant, such as hexagonal boron nitride (“hBN”).

The cBN is provided in an amount ranging between 10% and 43.75% (byvolume), and preferably 12% (by volume). Alternatively, diamond may beprovided in accordance with the foregoing range.

The cBN is dispersed in a resin bond, preferably a polyimide resin,constituting between 30% and 50% (by volume), and preferably 37.8% (byvolume), of the segment (excluding the volume percentage of cBNconstituting the segment). A glass frit, such as, for example,borosilicate glass, may be substituted for the resin bond.

The refractory, non-grinding abrasive grain, such as, for example, BC,is provided in an amount less than or equal to 10% (by volume), andpreferably 2.2% (by volume), of the segment (excluding the volumepercentage of the cBN constituting the segment). BC grain size ispreferably less than or equal to ½ the grain size of the average cBNgrain, and may be anywhere in the range between 220 and 1000 mesh.

The melt-phase metal may be selected from the class of copper-tin alloysknown as bronze, and constitute between 30% and 68% (by volume,excluding the volume percentage of cBN constituting the segment).Preferably, the melt-phase metal is composed of 34.3% (of the segment,by volume) of copper powder and 9.2% (of the segment, by volume) of tinpowder. The melt-phase metal serves to enhance heat dissipation throughthe segment during machining operations.

The dry lubricant is provided to inhibit the generation of heat due tofriction and constitutes at least 1% (by volume), and preferably 2.2%(by volume), of the segment (excluding the volume percentage of cBNconstituting the segment). The dry lubricant is preferably formed fromhBN, but it may alternatively be formed from molybdenum disulphide,graphite, coke or any lithium sterate.

Turning now to the composition of the matrix 40, the followingcompositions and ranges thereof are provided for the purpose ofillustration only. Generally stated, according to one aspect of thepresent invention, a grinding device is provided having a matrixsurrounding one or more abrasive segments, wherein the matrixcomprises: 1) an epoxy resin; 2) a dry lubricant, such as molybdenumdisulphide (“MOS”); 3) a porosity filler material, such as a ceramicmaterial shaped into spheroids; and, 4) a refractory non-grindingabrasive grain, such as silicon carbide (“SiC”).

The epoxy resin is preferably a two part epoxy with reactive dilutantand antifoam additives, such as, for example, a two-part epoxydistributed by The Dow Chemical Company or Midland, Mich., identified byDow product number 331/37-614. Preferably, the matrix comprises 35% (byweight) of the epoxy resin.

The dry lubricant is preferably MOS provided in an amount rangingbetween 1% and 5% (by weight), and preferably 1.7% (by weight). Similarto the dry lubricant provided in the segments, the dry lubricant isprovide in the matrix for the purpose of inhibiting the generation ofheat due to friction.

The porosity filler material is provided in an amount ranging between 3%and 15% (by weight), and preferably 7.0% (by weight). Preferably, thefiller is a 14/40 ceramic bubble material.

The refractory material is provided for the purpose of wear retardation,and is composed of an abrasive grain such as AlO3, SiC, boron carbide orzirconium oxide in an amount ranging between 10% and 70% (by weight),and preferably 56.3% (by weight). The grain size of the refractorymaterial preferably is the same size or smaller than the grain size ofthe cBN used in the segments.

Referring now back to FIGS. 1-3, one method for constructing thegrinding device 10 according to the preferred embodiment of the presentinvention will now be described.

A grinding device according to the present invention provides manyfeatures, benefits and advantages, including without limitation:improving safety of operation during high-speed grinding, increasingwheel “life”, increasing finish quality, reducing wheel dust,eliminating wheel dressing requirements and improving metallurgicalintegrity of the workpiece (i.e., no more than % negligible burns,stresses or other subsurface workpiece damage).

Referring now to FIG. 5, a device 100 according to one alternativeembodiment of the present invention takes the form of an annulargrinding wheel suitable for cylindrical machining operations to machinegenerally cylindrical workpieces, such as, for example, crankshaftbearings and pins, camshaft lobes, and the like. Device 100 includes acylindrical base 120, constructed from, for example, aluminum or steel,one or more abrasive segments 130 secured within an annular matrixcomposition 140 which at least partially surrounds an outer peripheralsurface 124 of the base 120. Segments 130 can be viewed as being“embedded” in the matrix 140 and may be integrally formed therein or maybe inserted into pockets (not shown) formed into the matrix 140 afterthe matrix 140 has been formed around (or otherwise secured to) the base120. Segments 130 are shown to have a thickness, which is for thepurpose of illustration only. Matrix 140 is shown to cover the entireperipheral surface 124 of the base, although it may alternatively coveronly a portion thereof. In either case, matrix 140 covers enough of thebase 120 and is of a sufficient thickness to surround each of thesegments 130 to prevent dislodging of the segments 130 during use.

Although the segments 130 are shown in spaced relation over only aportion of the periphery of the device 100, segments 130 may be spacedaround the entire periphery. Moreover, although segments 130 are showndepicted as circular “buttons”, they may alternatively take the form ofarcuate segments (not shown), whether spaced from one another by anominal distance or in an end-to-end abutting relation.

The composition of the segments 130 and of the matrix 140 according tothe present embodiment is the same as the composition of the segments 30and of the matrix 40, respectively, of the preferred embodiment hereof.

Devices 30, 130 according to the present invention are suitable forperforming dry machining operations on hard workpieces at feed rates inexcess of 40 meters/second. Indeed, it has been observed that the device30 according to the preferred embodiment hereof provides optimal drymachining operations at a feed rate of about 50 meters/second.

The present invention provides a grinding device, such as, for example,a surface grinding disc or an annular grinding wheel, wherein the deviceincludes a plurality of abrasive segments arranged in an array thereon(or therearound, as the case may be).

The present invention also provides a grinding device, such as, forexample, a surface grinding disc or an annular grinding wheel,constructed from a plurality of abrasive segments arranged in an arraythereon, wherein the abrasive segments include superabrasive particlesdispersed therein, and wherein the device is adapted to perform “drymachining” operations, that is, machining operations without the use ofmore than a nominal quantity of coolant or other lubricant.

The present invention even further provides a grinding device, such as,for example, a surface grinding disc or an annular grinding wheel,constructed from a plurality of abrasive segments arranged in an arraythereon, wherein the plurality of abrasive segments are embedded in amatrix composition adapted to enhance heat dissipation.

Even more, the present invention provides a method of dry machiningworkpieces wherein the method provides a grinding device, such as, forexample, a surface grinding disc or an annular grinding wheel,constructed from a plurality of abrasive segments arranged in an arraythereon, wherein the plurality of abrasive segments are embedded in amatrix composition adapted to enhance heat dissipation.

The present invention also provides a method of dry machining workpieceswith increased machining efficiency, that is, for example, by increasingworkpiece material removal rates.

The present invention even further provides a method of dry machiningworkpieces constructed from hard materials, which typically aredifficult to dry machine using known dry machining methods and devices.

Despite being adapted to perform “dry machining” operations, a grindingdevice according to the present invention will operate without any lossof function or benefit in a “wet machining” environment and the examplesused herein should not be interpreted as limiting the scope of thepresent invention to only “dry machining” operations or machiningenvironments.

While the invention has been described and illustrated with reference toone or more preferred embodiments thereof, it is not the intention ofthe applicants that the invention be restricted to such detail. Rather,it is the intention of the applicants that the invention be defined byall equivalents, both suggested hereby and known to those of ordinaryskill in the art, of the preferred embodiments falling within the scopehereof.

1. A grinding device, comprising at least one grinding segment and amatrix surrounding at least one of said at least one grinding segment,wherein: at least one of said at least one grinding segments is composedof a superabrasive material, a resin bond material, a refractorynon-grinding abrasive grain material, a heat-dissipative melt-phasemetal material, and a dry lubricant material; and wherein said matrix iscomposed of an epoxy resin, a dry lubricant, a porosity filler, and arefractory abrasive grain.
 2. The grinding device of claim 1, whereinsaid superabrasive material of said grinding segment is diamond.
 3. Thegrinding device of claim 1, wherein said superabrasive material of saidgrinding segment is cubic boron nitride.
 4. The grinding device of claim1, wherein said superabrasive material of said grinding segment isprovided in an amount between 10% and 43.75% (by volume) of the totalcomposition of the grinding segment.
 5. The grinding device of claim 4,wherein said superabrasive material of said grinding segment is providedin an amount of 12% (by volume) of the total composition of the grindingsegment.
 6. The grinding device of claim 1, wherein said refractorymaterial of said grinding segment is boron carbide.
 7. The grindingdevice of claim 1, wherein said refractory material of said grindingsegment is provided in an amount less than 10% (by volume) of the totalcomposition of the grinding segment.
 8. The grinding device of claim 7,wherein said refractory material of said grinding segment is provided inan amount of 2.2% of the total composition of the grinding segment. 9.The grinding device of claim 1, wherein a grain size of the refractorymaterial of said grinding segment is less than or equal to a grain sizeof superabrasive material.
 10. The grinding device of claim 1, wherein agrain size of the refractory material of said grinding segment isbetween 220 mesh and 1000 mesh.
 11. The grinding device of claim 1,wherein the melt-phase material of said grinding segment is a copper-tinalloy.
 12. The grinding device of claim 11, wherein the melt-phasematerial of said grinding segment is bronze.
 13. The grinding device ofclaim 1, wherein the melt-phase material of said grinding segment isprovided in an amount between 30% and 68% (by volume) of the totalcomposition of the grinding segment.
 14. The grinding device of claim13, wherein the melt-phase material of said grinding segment is providedin an amount of 34.3% of the total composition of the grinding segment.15. The grinding device of claim 1, wherein the dry lubricant of saidgrinding segment is hexagonal boron nitride.
 16. The grinding device ofclaim 1, wherein the dry lubricant of said grinding segment ismolybdenum disulphide.
 17. The grinding device of claim 1, wherein thedry lubricant of said grinding segment is graphite.
 18. The grindingdevice of claim 1, wherein the dry lubricant of said grinding segment iscoke.
 19. The grinding device of claim 1, wherein the dry lubricant ofsaid grinding segment is a lithium state.
 20. The grinding device ofclaim 1, wherein the dry lubricant of said grinding segment is providedin an amount at least 1% (by volume) of the total composition of thegrinding segment.
 21. The grinding device of claim 20, wherein the drylubricant of said grinding segment is provided in an amount of 2.2% (byvolume) of the total composition of the grinding segment.
 22. Thegrinding device of claim 1, wherein said resin bond material of saidgrinding segment is a polyimide resin.
 23. The grinding device of claim1, wherein said dry lubricant of said matrix is molybdenum disulphide.24. The grinding device of claim 1, wherein said dry lubricant of saidmatrix is provided in an amount between 1% and 5% (by weight) of thetotal composition of the matrix.
 25. The grinding device of claim 24,wherein said dry lubricant of said matrix is provided in an amount of1.7% (by weight) of the total composition of the matrix.
 26. Thegrinding device of claim 1, wherein said porosity filler of said matrixis a ceramic material shaped into spheroids.
 27. The grinding device ofclaim 26, wherein said porosity filler of said matrix is a 14/40 ceramicbubble material.
 28. The grinding device of claim 1, wherein saidporosity filler of said matrix is provided in an amount between 3% and15% (by weight) of the total composition of the matrix.
 29. The grindingdevice of claim 28, wherein said porosity filler of said matrix isprovided in an amount of 7% (by weight) of the total composition of thematrix.
 30. The grinding device of claim 1, wherein said refractorymaterial of said matrix is aluminum oxide.
 31. The grinding device ofclaim 1, wherein said refractory material of said matrix is siliconcarbide.
 32. The grinding device of claim 1, wherein said refractorymaterial of said matrix is boron carbide.
 32. The grinding device ofclaim 1, wherein said refractory material of said matrix is zirconiomcarbide.
 33. The grinding device of claim 1, wherein said refractorymaterial of said matrix is provided in an amount between 10% and 70% (byweight) of the total composition of the matrix.
 34. The grinding deviceof claim 33, wherein said refractory material of said matrix is providedin an amount of 56.3% (by weight) of the total composition of thematrix.
 35. The grinding device of claim 33, wherein a grain size of therefractory material of the matrix is equal to or small than a grain sizeof the superabrasive material of the grinding segment.
 36. The grindingdevice of claim 1, wherein the epoxy resin is a two-part epoxy withreactive dilutant and anti-foam additives.